Method and apparatus for the continuous performance monitoring of a lead acid battery system

ABSTRACT

The present invention concerns a battery monitoring system for monitoring a plurality of batteries serially connected to form a string. The battery monitoring system includes a number of probes connected to at least a portion of the string, a daisy chain bus having a select channel for serially interconnecting the probes, the bus having other, parallel channels for data communication and power, and a system server. The probes each have a sensing module and a communication module. The sensing module senses characteristics of at least a portion of the string, such as voltage or current. The communication module receives the sensed characteristics and converts them into digital form for broadcast to the system server over the bus. The communication module of the probes have a memory for storing an address assigned to the corresponding probe upon reception of an initialization signal sent by the system server via the bus. In order to readdress all of the probes, a reset signal is transmitted to all of the probes. The probes clear the present address, and wait until they are selected through the select channel. Once the probe has been selected, it receives an address from the system server, stores the address in its memory, acknowledges this to the system controller, and sends a signal on the select channel to the next probe. Accordingly, initialization of a battery monitoring system is easily performed. The invention also lies in an interface device for use with a battery monitoring system.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and apparatus for thecontinuous performance monitoring of a lead acid battery system, andmore particularly to such a method and apparatus which is easier toinstall and implement and provides added flexibility.

DESCRIPTION OF THE PRIOR ART

[0002] Lead acid batteries are a commonly used source of electricalenergy in the case when a main source, typically an AC supply line,fails. Typically, a bank of batteries will be interconnected in a systemconfiguration to provide the desired voltage and power for short termemergency situations, until the AC supply line is re-established oruntil a generator can provide the necessary power requirements. Suchsystems are often used as back-ups for hospital equipment,telecommunications equipment, computer equipment, etc.

[0003] However, battery systems represent what has been termed a bulletapproach, i.e. their performance is only truly evaluated when they arein use. This is a considerable inconvenience, since the reliability ofthe entire system is dependent on each of the batteries. Should thebattery system fail, this can lead to considerable monetary loss, andconsiderable loss of service with critical consequences, particularly inthe case of hospital equipment and telecommunications systems.

[0004] There are a number of symptoms which can be indicative of afailed battery. Some of these symptoms can lead to entire system failureand the requirement for premature (and costly) replacement. Onecondition in particular can create a dangerous situation for personsservicing the system or bystanders: thermal runaway. Thermal runaway isa critical condition arising during constant voltage charging in whichthe current and the internal temperature of a battery produce acumulative mutually reinforcing effect which further increases them andcan lead to the destruction of the battery.

[0005] There are a number of systems and devices on the market whichprovide either off-line monitoring or in service test. Depending on theprice and complexity level, each of these systems provide a more or lesscomprehensive evaluation of system performance. However, the presentsystems represent a relatively complex installation process and do not,according to the Applicant, provide continuous performance monitoring.

[0006] As an example of the present systems and the parameters which aremonitored, reference may be made to the following U.S. Pat. Nos.:4,707,795; 5,546,003; 4,916,438; 4,217,645; 5,206,578.

[0007] These systems generally provide sensing means at each battery,connecting each sensing means to a remote monitor through analogcommunication means such as a pair of copper wires and sensing a varietyof parameters for each battery. The remote monitor or the sensing meansdirectly perform calculations to extract from the sensed parametersvalues for indicia such as battery voltage, battery temperature, systemvoltage, ambient temperature, float current, AC component of the batteryvoltage, AC current component, etc. However, each of these systemsdescribes a complex installation process, and the installation of someof these systems may require taking the battery system off-line duringset-up which users do not appreciate.

[0008] It is also known in the art to measure a variety of parameterswhile charging, discharging, loading or using the battery system.

[0009] One of the parameters which can be useful to measure is thebattery impedance to provide an indication of the condition of thebattery. Typically, in order to measure the impedance, a current isimposed on the battery and the resulting voltage measured in order tocalculate the impedance since both voltage and current are known. Onesuch system for measuring the impedance of a plurality of batteries (noteach individual battery) is described in U.S. Pat. No. 5,281,920. Thesystem of this patent divides each string of batteries into two andapplies the current only to one half of the string. The disadvantagewith this system is that it is cumbersome to install, and the voltagethat is measured is done so for the totality of the half-string, not foreach individual battery and so is the resulting value for the impedance.

[0010] Accordingly, it is desirable to continuously monitor a batterysystem to provide adequate information in order to evaluate theperformance of the system and to perform preventive maintenance on thesystem.

SUMMARY OF THE INVENTION

[0011] It is an object of the invention to provide an interface devicewhich provides adequate information between at least a portion of astring of batteries serially connected and which can be easily installedwith a minimum of manipulation.

[0012] In accordance with the invention, this object is achieved with aninterface device for interfacing at least a portion of at least onestring of batteries with a battery monitoring system. The interfacedevice includes at least one probe means for respectively probing theportion of the at least one string, each of probe means including acontrollable sensing means for sensing a plurality of parameters of thecorresponding portion, a communication means for communicating data toand from the controllable sensing means, the data including controlsignals sent from the battery monitoring system to the controllablesensing means, and information signals relating to the parameters of thecorresponding portion that are selected by the control signals; and amemory for memorizing an address assigned to the corresponding probemeans upon reception of an initialization signal sent by the batterymonitoring system via the communication means. The interface devicefurther includes a bus for serially interconnecting the communicationmeans of each of the at least one probe means to the battery monitoringsystem in a daisy chain manner.

[0013] The invention is also concerned with a battery monitoring systemcomprising a plurality of interface devices and a system server.

[0014] It is another object of the invention to provide a batterymonitoring system which accurately and easily measures the batteryimpedance for each battery in a string of batteries. A corollary objectof the invention is to provide a method for measuring the batteryimpedance of a plurality of batteries serially connected to form atleast one string of batteries.

[0015] In accordance with the invention, this other object is achievedwith a plurality of batteries connected in series to form at least onestring of batteries; a plurality of probe means for respectively probingat least a portion of the at least one string, each of the probe meansincluding: a controllable sensing means for sensing a plurality ofparameters of the corresponding portion; a communication means forcommunicating data to and from the controllable sensing means, the dataincluding control signals and information signals relating to theparameters of the corresponding portion that are selected by the controlsignal; a bus for serially interconnecting the communication means ofeach of said at least one probe means in a daisy chain manner.

[0016] The battery monitoring system also includes a current injectionmeans connected to the at least one string for injecting a current inthe at least one string upon receipt of a control signal. The system isfurther provided with a system server connected to the bus andconfigured to select one of the probe means, to transmit control signalsto a selected one of the probe means and to receive information signalsrelating to the characteristics of the corresponding portion, memorymeans for storing the information signals, calculating means forcalculating a plurality of values relating to the characteristics andalarm means for raising an alarm when one or more of the values isoutside a predetermined range. The system server is operativelyconnected to the current injection means for sending a control signal tothe current injection means to inject a current in said at least onestring.

[0017] The invention further provides for a method for initializing eachprobe in a battery monitoring system, and a method for measuring theinternal impedance of a battery within a string of batteries.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] These and other objects of the present invention and itsadvantages will be more easily understood after reading the followingnon-restrictive description of preferred embodiments thereof, made withreference to the following drawings in which:

[0019]FIG. 1 is a schematic representation of a battery performanceprobe according to a preferred embodiment of the invention;

[0020]FIG. 2 is a schematic representation of a portion of a currentprobe according to a preferred embodiment of the invention;

[0021]FIG. 3 is a schematic representation of a portion of a rectifiervoltage probe according to a preferred embodiment of the invention;

[0022]FIG. 4 is a block diagram representation of a system serveraccording to a preferred embodiment of the invention;

[0023]FIG. 5 is a flow chart of the method for initializing a probeaccording to a preferred embodiment of the invention;

[0024]FIG. 6 is a flow chart of the method for scanning according to apreferred embodiment of the invention;

[0025]FIG. 7 is a representation of a digital word for use incommunicating sensed information in a probe to the system server;

[0026]FIG. 8 is a schematic representation of a discharge eventdefinition;

[0027]FIG. 9 is a schematic representation of a discharge event andenergy count; and

[0028]FIG. 10 is a schematic representation of a battery monitoringsystem according to one configuration of the invention, where only theserial interconnection of the select wire is shown.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0029] Traditional back-up battery systems comprise a plurality ofbatteries 3 connected in series to form a string 1. A back-up system caninclude more than one string 1 (although only one is shown in FIG. 1),depending on the power requirements of the user. Such an arrangement iswell known in the prior art.

[0030] A battery monitoring system according to the present inventionbasically comprises a number of interface devices including probe means10 and bus means 50 (shown in FIG. 1) and a system server 100. The probemeans 10 are individually connected to a corresponding portion of astring 1 of batteries 3, and are serially interconnected to the busmeans 50, which in the preferred embodiment of the invention is a daisychain bus having five wires, two of which are used for power 51, 52, oneis a broadcast out 53, one is a broadcast in 54 and one is a select 55.It should be noted that only the select 55 wire performs the serialinterconnection (as shown in FIG. 1), and the other four wires 51-54 area parallel connection.

[0031] The daisy chain 50 is connected to the system server 100, whichanalyses the information assembled by the probe means 10 and isprogrammed to trigger alarms and log historical data, among otherfunctionalities.

[0032] The system according to the invention provides for modularity, inthat any number of batteries 3 in any number of strings 1 may bemonitored. Furthermore, the final configuration of the batteries 3 to bemonitored does not need to be known prior to installation, and thesystem allows for additional (or less) batteries 3 than the originalconfiguration to be present in the strings 1, without having to spendtime and money reconfiguring the system i.e. manually and physicallyaddressing each of the probe means, as will be hereinafter explained.Furthermore, the system should not be interpreted as being limited tothe parameters hereinafter detailed, since the system is fully modularand reconfigurable, within the end user's specifications, so that one ora combination of parameters can be monitored.

[0033] To that effect, one of the main objects of the invention is toprovide for an interface device for interfacing at least one battery 3with a battery monitoring system, where each of the interface devices isconnected to a system server through a daisy chain bus, so that uponreception of an initialize signal, each interface device clears anaddress present in its memory. The system server then sends a signal tothe first interface device to set an address and transmit the address tothe system server. Once the address is received, the system server sendsa signal to the interface to deactivate or deselect itself and send asignal to the next interface device to be selected, and repeat theaddressing process until all interface devices have stored an address.

[0034] It should be noted that the select wire 55 is used exclusivelyduring the initalization phase. In broad terms, the battery monitoringsystem according to the invention operates in two modes: initializationand regular scanning. During the initalization phase, the system serversends out a reset signal via the broadcast out wire. This signaldeselects and resets all probe means connected to the daisy chain.Following the reset signal, the first probe means in the chain isselected by the system server through the select channel. The probe(already in the reset stage), receives an address signal from thebroadcast out bus and stores it in its memory. Once the address isstored, an acknowledge message is sent to the system server on thebroadcast in channel. The probe then de-selects itself and sends asignal of the select channel to activate the next probe in the daisychain. It should be noted that the next probe is selected by theprevious probe, and not by the system server. Using this sequence, thenext probe's address will be assigned in numerical order. The systemserver, in this case, controls only the probe acknowledgement coming viathe broadcast in channel. Once the last address in the chain isreceived, the system server selects the first probe in the next daisychain, if there is one, and performs the identical steps as above.

[0035] Accordingly, the system initialization is easily performed onceall of the interface devices have been connected to a respective portionof a string, and interconnected to a bus in a daisy chain manner.

[0036] Following the initialization phase, the system server switches tothe regular scanning mode. The difference between the initializationmode or phase and the regular scanning mode or phase lies in the factthat while all the probe means are de-selected and in listen mode, theprobe means that is being selected by the system server monitors thebroadcast in channel to see if it is being addressed. If the probe meansrecognizes its address, it sends an acknowledgement signal to the systemserver by repeating its address on the broadcast out channel. Followingthe address acknowledgement, the probe means then transmits to thesystem server the data monitored, as will be hereinafter detailed.

[0037] The invention also provides for a battery monitoring system sointerconnected.

[0038] The invention is also concerned with a battery monitoring systemfor measuring the impedance of a battery, where the system server isoperatively connected to current injection means. Each string in thebattery system is provided with a corresponding current injection means.Preferably, however, only one current injection means are used for allof the strings present in a battery system. When the system server sendsa signal to the current injection means, a current is fed to all of thebatteries in the string or strings simultaneously. The resulting voltageappearing at the terminals of each of the batteries is monitored by eachinterface device, and transmitted to the system server for calculation.The system server can then calculate the impedance of each of thebatteries in each of the strings. In a preferred embodiment, the currentthat is injected in each of the strings is an AC current, and morepreferably, an AC current having the shape of a sine wave.

[0039] Each of the components of the battery system will be hereinafterdetailed separately.

[0040] Interface Devices

[0041] Referring now to FIGS. 1-3, there is shown a schematicrepresentation of an interface device. The interface device basicallycomprises probe means and a bus. It should be noted that each portion ofa string of batteries is provided with its own probe. Each probe has acommunication module, a sensing module and an AC module.

[0042] As contemplated by the invention, three different types of probemeans can be used with a battery system: a battery performance probe, acurrent probe and a rectifier voltage probe. It should be noted that thecommunication module is identical for each of the three types of probes.It should be further noted that the battery performance probe and thecurrent probe are further provided with and have identical AC modules.In fact, the difference between the three types of probes lies only inthe portion of the sensing module that senses the variouscharacteristics of the portion of the string.

[0043] The communications module includes controller means, an analog todigital converter (ADC) and multiplexer (MUX) means. Preferably, the ADCand the MUX are integrated. The MUX has four analog inputs, hereinafterreferred to as channels 1, 2, 3 and 4, for receiving information fromthe sensing module.

[0044] The controller means are connected to the daisy chain throughoptical insulation means.

[0045] The sensing module has an analog front end, the analog front endbeing connected to the corresponding portion of the string and to themultiplexer of the communication means.

[0046] Each of the three types of probe means, and more specifically,each of the sensing modules will be detailed hereinafter.

[0047] Battery Performance Probe

[0048] The battery performance probe measures the performance of eachindividual battery in the battery system, and measures the followingparameters: battery DC voltage, temperature of the negative terminal ofthe battery and AC voltage drop during impedance measurements.Accordingly, the respective portion of the string to which the batteryperformance probe is connected is the positive (PT) and negative (NT)terminals of the battery to be monitored.

[0049] Analog Front End (or Sensing Module)

[0050] The analog front end or sensing module of the battery performanceprobe includes a protection circuit consisting of a fuse F1 and a Zenerdiode D1. The fuse is connected to the PT of the battery and ispreferably a Polly switch with 90 mA hold current. The fuse will beactivated in the following cases: when a short circuit increases theprobe's input current; when the battery voltage exceeds the Zenervoltage of diode D1 (i.e. 16V); or when the PT and NT terminals arereversed.

[0051] Such an arrangement exhausts all possible scenarios of probefailure. In all cases, when the F1 current increases above the triplevel (200 mA), the Polly switch will heat up thereby causing the fuseresistance to increase approximately 5 times its magnitude. Once thefailure current returns to normal operating values, the fuse cools downand its resistance is reduced to a very small value. Consequently, anyvoltage exceeding 16V is clamped to the value of the Zener diodevoltage. This is also true for a reversed voltage, but the input voltageis now clamped to the forward voltage value of the Zener diode.

[0052] The positive terminal of the battery is further connected to avoltage divider network R1 and R2, which preferably divides the inputvoltage by 3 in order to adjust the ADC input voltage to match that ofthe battery. The division by a factor of 3 has been chosen to fit amaximum range of battery voltages (up to 15 V DC) to the maximum inputvoltage for the MUX/ADC, i.e. 5 V DC. Preferably, since resistors R1 andR2 create an input path between the negative and positive terminals ofthe battery, an additional protection is provided by using R1 as atwo-part resistance, one created by an overrated (0.5W) power,flame-proof resistor and the other one by a regular SMT resistor.

[0053] The voltage divider circuit is followed by a low pass filter toeliminate high frequency components. The cut-off frequency of thisfilter preferably approximately 5 Hz, which is sufficient for mostapplications since the 60 Hz component (typical for industrialapplications) does not exceed 10% of its original value. The output ofthe low pass filter is connected to channel 2 of the multiplexer so thatthis channel monitors the DC voltage of the battery under test.

[0054] The negative terminal of the battery is connected to a thermalprobe, the circuit of which is illustrated on FIG. 3 (the thermal probecircuit is identical for the rectifier voltage probe and the batteryperformance probe). The thermal probe includes a thermistor R_(T) with a5K resistance at 25° C. is used as a thermal sensor. The resistancevalue of the sensor drops with increased temperature causing voltageacross the positive and negative terminals of the battery to dropaccordingly. The combination of the resistor RP, the capacitor C4 andthe resistance R_(T) creates a filter with cut-off frequency atapproximately 33 Hz. This threshold eliminates the noise caused by thedigital signal processing switching as well as generated to the batteryduring impedance measurements. The output of the thermal probe isconnected to channel 3 of the MUX so that this channel monitors thebattery's internal temperature. Since the thermistor is a non-lineardevice, a lookup table is used to calculate the real temperature. Itshould be noted that the repeatability of the thermistor characteristicis better than 0.2° C. for the entire range between −10° C. and 75° C.

[0055] AC Conditioning Section

[0056] In order to provide accurate measurements relating to ACcomponents, the probe means further includes an AC conditioning section(or AC module), to condition the peak voltage used for calculating theinternal impedance of the battery. This section consists of an inputband-pass filter, followed by a peak detector and a low-pass filter.

[0057] The AC input to the filter section is connected via resistor RAC,in order to protect the filter input circuitry in the case of aninternal short in the AC section. The resistor preferably has a value of33.2K and is preferably rated as a flame retardant 300V DC resistor with500 mW power dissipation. This arrangement provides an additionalprotection for the input of the AC section which is normally notprotected by the fuse F1.

[0058] The input band-pass filter consisting of a resistor and capacitornetwork has a center frequency set at preferably 60 Hz with a resolutionof ±0.1 Hz. Preferably, the 5% bandwidth is 0.3 Hz thus providingexcellent attenuation of 2^(nd) and higher harmonics. The filter'sfrequency stability is achieved by preferably using ultra stableCOG-type capacitors. The DC reference for the filter is set by theresistors at approximately 3V. Since the amplifier is powered by thebattery voltage of 12V, the filters uses the full swing of ADC input(approximately 2V above reference voltage). At a band-pass filter gainpreferably set at 65.65, the input AC voltage is approximately 14 mVpeak to peak of RMS value of input AC voltage. The DC reference voltageis connected to channel 4 of the MUX via the low-pass filter with acut-off frequency of preferably 1.7 Hz. This voltage is used as the DCreference, subtracted from the peak voltage.

[0059] The output of the band-pass filter is connected to a peakdetector. The diode Dp charges capacitor Cp up to peak value during apositive peak (which is the actual value above DC reference). During anegative peak, the capacitor is discharged via a resistor. Since theproduct of the resistor and the capacitor is much larger than 17 ms({fraction (1/60)} Hz), the voltage drop on the capacitor is very smallduring the time between two subsequent peaks. This voltage is connectedto channel 1 of the MUX via a low-pass filter with a cut-off frequencyof preferably 1.7 Hz. This low-pass filter eliminates the ripples in thevoltage caused by the discharge of the capacitor.

[0060] It should be noted that the AC channel accuracy depends on thesensitivity threshold of the entire AC section. Assuming a requiredaccuracy of 1%, at least 100 bits of the channel 1 of the MUX must begenerated. At 1.220703 resolution of the ADC converter, the minimuminput voltage has to be at least 1.3 mV of RMS value. Practically, dueto additional errors of the ADC conversion (due to linearity, thermaldrift, etc.) the minimum required input voltage is approximately 3 mV.This number has to be used when calculating the minimum required ACcurrent for selection of the current transmitter.

[0061] It is important to note that the analog section of the probemeans is powered by the tested battery voltage for 6-cell batteries. ADC/DC up-converter must be used in the case of 1 to 3 cell batteries.

[0062] Rectifier Voltage PROBE

[0063] In order to evaluate total system performance, the batterymonitoring system according to the invention can further include arectifier voltage probe, which is used to monitor the voltage andperformance of a single string. Accordingly, the voltage input isconsiderable (can be up to 600V), and the sensing module thus isdifferent from the sensing module of the battery performance probe,although the function is the same. It should however be noted that therectifier voltage probe does not monitor the AC components, so that eventhough the circuitry may be present, it is deactivated.

[0064] A system voltage probe, designated as RVP features single channelinput with two ranges: 600 V and 150 V. The analog front end of theprobe operates identically as with the battery performance probe, butwith a slightly different signal conditioning circuitry (shown on FIG.3). The R1′ and R2′ resistors divide the input voltage to a levelsuitable for ADC conversion (max. 5V). The input of the probe isprotected by two series, high voltage flame proof resistors (total ofapproximately 2 Mohms for 600V probe and 1 Mohm for 150 V). The low passfilter has a cut-off frequency of 10 Hz to filter out any AC componentsin the rectifier voltage output, and the resulting voltage is applied tochannel 2 of the MUX.

[0065] The resistor R1′ provides protection against eventual shortcircuits inside the probe. The value of this resistor will be dependenton the probe's range. The reliability of the protection of the circuitis ensured by the use of two 0.5W, flame proof resistors which make upresistor R1′. Preferably, the analog circuitry of the probe is poweredby the DC/DC converter from the system server (as shown in FIG. 1).

[0066] As above, channel 3 of the MUX is used to perform ambienttemperature measurements. It should be noted that the thermal probecircuit is identical for that of the battery performance probe, but thatthe thermal probe is not connected to a negative terminal of a battery,but is located outside, in order to monitor ambient temperature.

[0067] Current Probe

[0068] The current probe is connected in series with any one string andis used to measure the charge/discharge current, float current and theAC component of the string current during impedance measurements.

[0069] The current is measured through a voltage drop across a shuntresistor. Since a standard 100 mV shunt resistor is used, the range ofthe current node depends on the shunt nominal current. Once the range ofthe current node is selected, the shunt voltage conversion factor fordifferent shunts is programmed in the server's memory.

[0070] The same shunt resistor is used to measure charge/discharge,float and AC current measurements. The circuitry is shown in FIG. 2.

[0071] The shunt resistor is placed in series anywhere in the string tobe monitored, and the input terminals of the current probe are connectedon either side of the shunt resistor (see FIG. 2).

[0072] The current analog front end, or sensing module, consists of aninstrumentation amplifier for a first stage of the signal conditioning.Resistor Rg sets the amplifier gain at 12.207. Since the ADC resolutionis 1.2207 mV per bit and the shunt voltage is 100 mV, the amplifierresolution is thus 0.1 A/bit. The middle point between charge anddischarge (zero level) is set by a reference voltage equal to 2.5000V. Acharge current will increase this value, while a discharge current willdecrease this value, by an amount proportional to the measured current.

[0073] The output signal is filtered by a low-pass filter consisting ofRf and Cf components, and having a cut-off frequency of 5 Hz.

[0074] The various ranges for the current node have been obtained bycalculating in the server the various conversion factors. This type ofnode is used for currents up to 1500 A which is the maximum range forcharge/discharge current. An additional stage of shunt voltage is usedfor the float current measurements, as illustrated in FIG. 2.

[0075] The difference lies essentially in instrumentation amplifiergain, voltage reference and additional amplifying stage. Since the floatcurrent has only a positive polarity, the reference voltage is set at alower value in order to compensate for offset voltage, as well as toincrease the range available for the relatively small float current. Thegain for the float current channel is approximately 1000. Thus, theabove mentioned principle is used for a shunt current of up to 500 A,thereby providing a maximum resolution of 2.3 mA/bit. As before, thelast stage of the float current channel is a low-pass filter with acut-off frequency of 5 Hz.

[0076] The third channel of the current node measures the AC componentof the shunt current, and is used for eventual internal impedancemeasurements. This channel is illustrated in FIG. 1, since it isequivalent to the AC conditioning section of the battery performanceprobe. However, since the input signal is taken from the first stage ofthe instrumentation amplifier, the total gain of the channel is 12.20703times larger than that of the Battery Performance node. This featureallows for the measurement of relatively small AC components during theimpedance measurement routine.

[0077] Supply and Reference Section

[0078] The supply and reference section, although illustrated only forthe battery performance probe, is identical to each of the three typesof probes.

[0079] In order for the digital components (as well as the analogcomponents) to be properly powered and the reference voltagesnormalized, the interface device includes a supply and referencesection. This section consists of a linear voltage regulator and a shuntdiode type reference. The linear voltage regulator uses a standard fix5V regulator to power the microcontroller and optocouplers. The totaloutput power capability is preferably in the range of 100 mW.

[0080] The reference section uses a shunt diode voltage reference. Theprecise output reference is set by a voltage divider. The +5V referenceis set with a resolution of ±1 mV, and is used as the reference and forVCC for the ADC conversion.

[0081] Both supply and reference voltages use the battery's outputvoltage. The minimum voltage required to supply the probe means is 7.5V,but a typical value is 13.5 VDC for a fully charged battery in floatmode.

[0082] ADC Conversion SECTION

[0083] The ADC section for each of the three types of probes areidentical.

[0084] Since the various parameters that are measured by each of thethree types of probes produce analog values, and in order to permitaccurate calculations, the parameters must be converted into digitalvalues. To that effect, the probe means, as mentioned above, include ananalog-to-digital converter. The ADC is preferably an LT1594 ADCconverter, which is a four channel, 5V micropower, 12 bits samplingconverter. However, it should be readily apparent that any otheranalog-to-digital converter can be used. Since the reference voltageused is 5V, the resolution of the converter is 1.220703 mV at the inpurof the ADC's multiplexer. The effective resolution of the DC input(channel 2) is 3 times this value, or 3.67 mV. For a typical value of13.5 Vdc battery voltage in float mode, the error is approximately0.03%. However, due to other factors, such as temperature drift of thevoltage divider, inaccuracy of adjustments, etc., the effective errorclaimed for this measurement is 0.2% for the entire range of batteryvoltages (from 7.5 Vdc to 15 Vdc), and 0.15% for the typical range of 12to 15 Vdc.

[0085] It should also be noted that the operation of the ADC iscontrolled by the microcontroller.

[0086] Controller Means

[0087] The controller means handle the digital data processing in thecommunication means, and essentially provides for communication with thesystem server via the broadcast in and broadcast out channels, controlsthe MUX and ADC, following the various measurements compiles the digitalword to be sent to the system server and performs general housekeepingfunctions such as checksum generation, LED control, etc.

[0088] An important feature of the controller means is that they canlisten to the broadcast in bus, and include memory means for storing anaddress. At all times the controller means listen to the broadcast inbus in order to recognize at least one of two signals: a reset and anaddress. Following the reset signal, the controller means clears theaddress within its memory and waits to be selected by the select channelbefore responding.

[0089] Once the system is initialized and in monitoring mode, thecontroller means listen to the broadcast in channel to see if itsaddress is on the bus.

[0090] Thus, when the controller means receive a selection signal fromthe system server in the form of its address on the broadcast inchannel, the controller means generate an acknowledgement signal andgenerate a MUX address to select an analog signal connected to the inputof the multiplexer. The analog signal is converted into digital form bythe ADC. The same process can be repeated for each of the MUX channels.Alternatively, the selection signal can include a sub-signal identifyingonly one channel for which a reply is required by the system server.

[0091] The digital signal is then packaged by the controller means intoa digital word which consists of 19 hexadecimal characters asillustrated in FIG. 7. The first two digits are the probe address, thenext three are the digital data from channel 1 of the MUX, the nextthree are the digital data from channel 2 of the MUX, the next three arethe digital data from channel 3 of the MUX, the next three are thedigital data from channel 4 of the MUX, the next two are a checksumgenerated by the controller means to ensure data integrity and the lastdigit is representative of the probe status. It should be noted thatother formats for the digital word can be used, and are all within theskill of a person expert in this field.

[0092] The controller means also include a clock which is generated byan external crystal oscillator with a resonant frequency of preferably 4MHz. A resistor network provides for pull-up for incoming signals.Additional resistors can be used to provide for current limitingfeatures when the controller means control the optocouplers. Anotherresistor is used, and its value is dependent on the application of theprobe means.

[0093] Since the probe means can be connected to different levels ofsystem voltage, there must be insulation means between the processormeans and the bus, preferably in the form of dual optocouplers.Preferably, each section of the optocouplers insulates one channel ofthe bus. The preferred optocouplers have breakdown voltages of 2500V DCapplied during a one second period.

[0094] Each probe means is also preferably provided with LEDs to informa user on the actual status of the processor. The configuration that hasbeen chosen is the following: if the LED is off, the probe is notpowered or not selected and is in waiting mode. If the LED is flashingat a frequency of approximately 2 HZ, the probe has been resetted and iswaiting to be addressed. If the LED is off, the probe has been selected,but a response has not been sent due to faulty conditions. Finally, ifthe LED is flashing with a periodic on time of 0.5 sec, the probe isselected and operates properly. It should also be recognized that otherconfigurations for visual indication of probe status can be used.

[0095] System Server

[0096] As mentioned above, the system server provides the interfacebetween the probe means, system peripherals and the customer interface.The system server collects the data monitored by the probe means,performs digital data processing, including the required calculations,and provides information to a user via communications interfaces.

[0097] A block diagram of the system server is shown in FIG. 4. As canbe seen, the system server includes a central processing unit (includingmemory means), communications modules for connecting system connectorssuch as a local rectifier voltage probe, a local modem or a TCM module,for connecting a bi-directional communication port such as an RS232port, a modem circuit for connecting an external modem, an equipmentwatchdog circuit (for indicating equipment failures). The CPU is alsoprovided with an auxiliary input-output driver which drives alarm relaysand visual indicators. The bus is directly connected to the CPU. The CPUallows for customer alarm inputs, which are fully configurable.Evidently, the system server also includes power up means and resetmeans.

[0098] The system server can thus communicate with the outside world viathe RS232 port. Alternatively, the system server can be accessed via alocal computer, such as a laptop, a hand-held PC unit including akeyboard, or a modem.

[0099] In a preferred embodiment of the system server, the CPU can beone of two microcontrollers manufactured by Dallas Semiconductor. TheDS2252(T) model can be used for the regular version of the systemserver, consisting of all of the above functions of the system. Thismicrocontroller is an 8051 compatible microcontroller based onnon-volatile RAM technology. This chip has been designed for systemsthat need to protect memory contents from the disclosure, so that anyperson attempting to tamper with its contents will trigger themicrocontroller to erase the memory contents, or otherwise deny accessthereto. Alternatively, the DS5000(T) model can be used in reduced costversions of the battery monitoring system. This model however does notprovide access with a hand-held unit, nor does it support impedancemeasurement of each batteries in the system. This chip is a 8051 fullycompatible 8-bit CMOS microcontroller that offers softness in allaspects of its application. This is accomplished through thecomprehensive use of non-volatile technology to preserve its content inthe absence of Vcc.

[0100] The processor means preferably operate with a 11.0592 MHz clock.

[0101] The system server features a standard (or monitoring) mode ofoperation, and an active mode of operation. In the standard mode, thesystem server performs only passive monitoring of the system'sperformance. In the active mode, the server performs monitoring as wellas provides feedback to the system rectifier if either different thermalambient conditions are monitored, or thermal runaway is detected.

[0102] The system server's standard mode of operation includes systemhousekeeping and monitored data processing, such as measurements,calculations, alarms and data storage. Both of these operatesimultaneously during the interrupt routine, however each mode will bedescribed separately.

[0103] System Housekeeping

[0104] The system housekeeping operation includes system configuration,reset function, system initialization, equipment failure detection,auto-call management, time keeping and database management.

[0105] The fact that the system according to the invention is modularrequires that configuration information be provided in the systemserver's internal memory. The configuration data includes siteidentification, number of probes (up to a maximum of 255), number ofcells per battery (1 to 6), number of strings (1 to 5), number ofcurrent probes (1 to 5— same as the number of strings), number ofbattery probe means (up to 255), rectifier voltage probe presence,ambient temperature probe presence (YES/NO), customer alarm inputactivation (ON/OFF for each customer alarm input) and buzzer status(ON/OFF). It should be noted that the above numbers for the varioustypes of probe means are for the preferred embodiment of the invention,but that increased numbers, and thus increased modularity, can easily beintegrated by adding memory and software for controlling the variousadditional components.

[0106] The battery monitoring system according to a preferred embodimentof the invention can have a plurality of configurations. In a simpleconfiguration, as that shown in FIG. 10, the back-up battery systemcomprises only one string of ten batteries. Each of the batteries isprovided with a battery performance probe. The string is provided with ashunt resistor in series with the string, to which is connected acurrent probe. The total string is also provided with a rectifiervoltage probe, in order to measure ambient temperature and total stringperformance. This setup would then have 12 probe means, all seriallyconnected to three daisy chains: battery daisy chain (here 10 probemeans); current daisy chain (here 1 probe means, but can be up to 5);and auxiliary daisy chain (here RVP). The split into three daisy chainsis preferable in order to reduce the high power requirements to theoutput driver. For ease of clarity, only the serial interconnection ofthe select channel have been shown on FIG. 10. It should further bereadily apparent that a battery monitoring system according to thepresent invention could be limited only to battery performance probes(in order to monitor only the DC performance of each of the batteries),or could be further provided with a current probe for each of thestrings (thereby permitting the monitoring of the internal impedance ofeach of the batteries), or could be further or alternatively providedwith a rectifier voltage probe for each of the strings, in order tomonitor ambient temperature and therefore thermal runaway.

[0107] The configuration information can be uploaded to the systemserver's memory locally via a portable terminal or remotely via a modemand a remote PC.

[0108] The reset function, which effectively clears the configuration ofthe system server's memory, is performed in the following cases: during“Power On” routine, so that each powering up of the system first resetsall probes, then re-addresses them and verifies what equipment, if any,is connected to the RS232 port; on request by pressing the RST buttonprovided on the system server; and remotely via a command sent throughthe RS232 port—this type of reset, usually referred to as a soft reset,resets all probes, but does not verify which equipment is connected tothe RS232 port.

[0109] Following each reset, the addresses of all of the probes areerased and the system initialization process is performed (see FIG. 5).

[0110] The initialization process includes the following steps:

[0111] review the actual system configuration stored in the systemserver's memory;

[0112] send a reset request to all probes, after which each probe erasesits address and sets itself to listen mode;

[0113] verify the number of probes connected to each input of theserver, if the verified configuration agrees with the storedconfiguration, continue with initialization process;

[0114] select the first probe by setting a low voltage on the firstprobe select channel;

[0115] by the probe, sending an active state confirmation to the systemserver via the broadcast in channels;

[0116] if the active state confirmation is not received within aspecified time frame, of the received data is corrupted, the systemserver stops the initialization process and sends a “Probe #error—initialization fail”;

[0117] if the active state confirmation is correct, the system serversends the first address to the first probe;

[0118] the probe registers this address in its own memory and sends anacknowledgement to the system server via the broadcast in channels;

[0119] if the response is not received within a specified time of thereceived data is corrupted, the system server stops the initializationprocess and sends a “Probe # error—initialization fail”;

[0120] if the response is correct, the system server sends a message tothe probe to de-select itself and select the next probe in the daisychain;

[0121] the first probe de-selects itself and selects the next one in thechain by setting a low voltage on the select channel;

[0122] repeat the steps for addressing for each subsequent probe in eachstring;

[0123] after the last probe has been addressed, the system server sendsa message to the computer “server initialized successfully”, and thesystem server switches to regular scanning mode.

[0124] Using the above process ensures that a failed or absent probewill be quickly identified in the chain when the response signal is notreceived by the system server. In such a case, the system server stopsthe initialization process and raises an alarm. The initializationprocess will be halted until the problem is fixed or a new configurationis programmed by the user.

[0125] It should be noted that the above process identifies only nodeswhich communicate with the system server using the controller'sprotocol. Hardware, which does not perform digital communication, willnot be identified during the initialization process. This might resultin an erroneous reading, for example a reading of 0° C. if thetemperature sensor is not present.

[0126] The regular scanning mode is performed during normal monitoringprocess (if no special routine request is received), and includes thefollowing steps (see FIG. 6):

[0127] when the initialization has been successful, all of the probesare de-selected and are in listen mode;

[0128] the system server sends an address of a probe to be selected onthe broadcast out channels;

[0129] the probe that recognizes its own address changes its status toactive mode;

[0130] the probe sends an acknowledgement signal via the broadcast-inchannels to the system server; the confirmation consists of the probe'saddress;

[0131] if a response from the probe is not received within a specifiedtime frame, or the data is corrupted, the system server stops theprocess and initializes the probe verification subroutine;

[0132] once the probe is active, the local parameters are monitored, theinformation is packaged into a digital word, and the digital word issent to the system server via the broadcast-in channels;

[0133] if the data is not received within a specified time frame, thesystem server stops the process and initializes the probe verificationsubroutine;

[0134] if the received data is corrupted, the system server ignores thedigital word and continues its regular operation; however, theinformation about the corrupt data is stored in the system server'smemory; if the data is corrupt three times in a row, the message “Probe# fail” is recorded and an equipment alarm message is logged into thealarm log;

[0135] if the received data is correct, the system server sends amessage to the probe to de-select itself and go off-line; at this point,the digital word is processed within the system server's processor;

[0136] the next probe's address is selected, and the process repeatsitself;

[0137] following successful data processing from all of the probes inall of the strings, the cycle is repeated again starting with the firstprobe, at whatever frequency is specified by the user.

[0138] Equipment failure detection permits the system server to detecthardware malfunction and report it to the user via the Equipment FailureAlarm (EFA). Since this type of failure practically eliminates thesystem from operation, the EFA alarm is classified as Major. The EFAsection of the software programmed into the system server performs thefollowing operations:

[0139] the system server monitors probe performance via the probe'sresponse on the broadcast in channels; if a response is not received,the software stops addressing the following probes and repeat therequest for data three times approximately 1 second apart; lack of aresponse during subsequent calls generates an error message providingthe address of the probe which did not respond;

[0140] following verification of a not responding probe, the systemserver selects the next address in the chain; if the failure of theprobe is due to a break in the chain, each subsequent probe will bedeclared as failed; following verification of the last probe in thechain, the system starts this operation all over again;

[0141] if the failure of a probe is due to a probe malfunction causingit to broadcast corrupted data, the following probes will performcorrectly; the system server will scan all remaining probes as duringnormal operation until it reaches a faulty probe again;

[0142] during operation when there is a modem connected to the systemserver, the controller monitors the presence of the modem on the RS232port; if the modem signal is lost, the system server continuesmonitoring until the signal is detected again; following signaldetection, the system server sends an initialization string to the modemin order to establish proper communication via a telephone line, awireless link or an optical link.

[0143] The system server also includes an auto-call function. It canstore up to three different telephone numbers each of up to 10 digits.The auto-call function is initiated by a Major Alarm. Once this priorityof the alarm is detected, the system server will initiate the auto-callfunction by dialing the first telephone number in the hierarchy. If thisfirst number does not respond, the second and then the third number aredialed. The system server will retry each of the telephone numbers inorder until successful communication is established and the properinformation is sent to the remote monitoring station.

[0144] In order to properly organize the data within the database, thesystem server also includes a time-keeping function, in a proper format.

[0145] As mentioned previously, the system server stores various events,parameters, calculations, alarms, etc. in a database. The databaserecord consists of the name of the event, for example system overcharge,the actual value of the parameter over the set point, the time of theevent, the alarm priority and the alarm status. In the preferredembodiment of the invention, the system server's database can store upto 1500 events. Once the events are reviewed or rewritten to a central,user database, the database can be cleared.

[0146] After having received the digital word from a given probe, thesystem server performs data processing on the information received inorder to perform a number of measurements and calculate a plurality ofvalues.

[0147] In broad terms, the system server will measure battery voltage,battery temperature, system voltage, ambient temperature, dischargenumbers, float current, AC voltage of the battery and AC currentcomponent. It should be understood that not all of these measurementsneed to be performed, and that additional measurements can be performedif so required, depending of the user's needs, and as long as the propercombination of probe means are present in the final configuration forthe battery monitoring system. Each of these measurements will bedescribed separately.

[0148] Battery voltage is measured by the Battery Performance Probe. Theresolution of the measured voltage is approximately 3.6 mV. However, dueto other factors such as temperature drift, component tolerance, etc.,the combined error is ±10 mV. Once the battery voltage reading is sentto the system server, the controller compares the value with a pre-setvalue to determine whether an alarm should be raised if the measuredvalue exceeds a predetermined range. For example, the system will raisean alarm is the battery is overcharged, undercharged or discharged. Ifan alarm condition is detected, the system sets an alarm priority andthe alarm is logged into the system server's database.

[0149] Battery temperature is measured by the thermal sensorencapsulated in the negative terminal of the Battery Performance Probe,as mentioned above. The thermal sensor is connected to the negativeterminal of the associated battery, so that the temperature inside thebattery is transferred to the thermal sensor. The time constant of thesensor is approximately 5 minutes, so 1% is achieved after approximately25 minutes in transient conditions.

[0150] The thermal sensor, as explained previously, uses an NTCthermistor with screened characteristics to achieve the 0.2° C.repeatability over the entire range of −10° C. to +75° C. Since thethermistor has a non-linear thermal curve, the output voltage iscompared with a look-up table stored in the system server's database (inthe standard system server case), or is calculated from an equation inthe PC software case. It should be noted that the combined error of thethermal channel is ±0.5° C.

[0151] The internal temperature of the battery can be displayed on a PCscreen in the direct mode of operation. Otherwise, in a data processingmode of operation, the internal temperature is compared with the ambienttemperature. If the internal temperature exceeds the ambient temperatureby a predetermined amount, a thermal runaway is declared, the alarmmessage is logged into the database and a LED on the front of thefaceplate is activated. Since a thermal runaway will usually haveassigned a Major alarm, the system server also initiates the auto-callfunction.

[0152] The total system voltage is measured by the Rectifier VoltageProbe. As explained above, there are, for the system of the invention,two types: one to measure system voltages in the range of 20 to 150 Vdc,and another to measure system voltages in the range of 100 to 600 Vdc.As also mentioned above, the input of the Rectifier Voltage Probe isprotected by overrated, flame proof, high voltage, 2 Mohm serialresistors. It should be noted that the signal processing of theRectifier Voltage Probe is identical to that of the Battery PerformanceProbe, and that the combined error in both cases is better than 0.1%across the entire range of the Probe.

[0153] The voltage read by the RVP is compared with a set ofpre-prograrnmed set points, such as system overcharge, systemundercharge, system discharge. If alarm conditions are detected, analarm message, along with the associated data, is logged into the systemserver's database, and a LED corresponding to a pre-set priority isactivated.

[0154] In order to compare the internal battery temperature with theambient temperature, two different types of sensors can be used. Thefirst, and most simple, is the thermal sensor connected to the RVP. Thissensor will be used when all of the batteries being monitored arelocated in only one area, such as when all of the batteries are locatedin a single cabinet, or when an RVP function is installed in the systemserver's hardware. The second, and more complicated, can measuretemperatures in up to four different areas (convenient for submarines orother installations where the batteries are scattered). The secondalternative requires that each thermal sensor have batteries associatedtherewith, so that the proper comparisons can be made.

[0155] Since the thermal sensor is identical to that of the BatteryPerformance Probe, the same signal processing is performed. In additionto thermal runaway detection, ambient temperature is also used to detectabnormal temperatures in the area where the batteries are located, andthis can generate an ambient temperature alarm (for example, if thecooling system fails, since battery reliability decreases with increasedtemperature—in this case, batteries are more susceptible to thermalrunaway).

[0156] Another parameter which is useful for evaluating a battery is thedischarge number count. This function measures the number of dischargeswhich have occurred since the initialization of the system, or since thesystem has been monitored. A discharge event is measured on the basis ofthe definition presented on FIG. 8. Accordingly, a discharge event isdeclared when the current value exceeds a pre-set discharge currentlevel (event #1). As long as the current level remains in the dischargearea, no new discharges can be declared. However, once the currentcrosses the zero level, identified as the discharge cancellation point,and move into the charging zone, the discharge number count is ready todeclare the next discharge event which will occur when the current againcrosses the discharge current level (event #2).

[0157] Preferably, the discharge events are classified into twocategories, i.e. short and long duration. The user has of course theoption of setting the period of time for the “short discharge duration”.If the duration of the discharge is less than a pre-set value, thedischarge event is accordingly logged into this category and can bedisplayed on a screen accordingly. Discharges which are longer than thispre-set value are combined with the short discharge events in order toevaluate overall system discharge. In a preferred embodiment of theinvention, the data that is displayed is the total number of dischargesand the number of short duration discharges.

[0158] The battery monitoring system can also include a current probe.Another parameter that is measured is the float current. Since the floatcurrent is measured using the same shunt resistor as that for thecharge/discharge current, the resolution is considerably affected by theshunt. In a basic configuration (100 A shunt), the resolution isapproximately 2.7 mA/bit. If the shunt range increases, the shunt'sresistance decreases and the resolution decreases by a proportionalamount. Thus, for a 500 A shunt, the resolution is 5.5 mA/bit, whereasfor a 1000 A shunt, the resolution is 10.8 mA/bit. The total range ofthe float current channel is 2.5 A, so that if the float current exceedsthis value, the system server's mode of operation automatically switchesinto charge mode.

[0159] As also mentioned previously, each battery probe means hasassociated therewith one channel to measure the AC voltage drop acrossthe battery. This channel is used to measure the AC voltage following anAC current injection into the battery system. The range of this channelis 0 to 20 mVpp, and although the measurements of this channel areperformed during every cycle of the probe's scan, the system server willuse this data only following an impedance measurement request, triggeredautomatically or manually. Otherwise, this data is ignored.

[0160] The AC current is also measured by the current probe. The ACcurrent signal is extracted following the first stage of currentamplification and then applied to the AC channel identical to that ofthe battery probe. Further processing of the AC signal in the currentprobe is done in the same manner as for the battery performance node.The range of AC current measurements is from 0.4 App to 3.5 App.Although, as above, the measurement is performed during every cycle ofthe probe's scan, the AC current component is used by the system serveronly following an impedance measurement request. Otherwise, this data isignored.

[0161] The above parameters are measured by a respective probeassociated with a respective portion of a string of batteries and thenused to perform various calculations in order to evaluate systemperformance, such as battery differential temperature (used to trigger athermal runaway alarm), battery impedance and total energy discharged.

[0162] The battery differential temperature is calculated to trigger athermal runaway condition. The battery temperature, measured by theBattery Performance Probe, is subtracted from the battery ambienttemperature. If the difference exceeds a pre-set value, a thermalrunaway condition is declared and the appropriate alarm is raised. Ifthe monitoring system monitors more than one ambient temperature, in thecase where the batteries are located in more than one area, the batterydifferential temperature is of course measured with respect to theassociated ambient temperature, i.e. the internal temperatures of thebatteries located in cabinet 1 are compared against the ambienttemperature of cabinet 1 only.

[0163] In order to perform battery impedance calculations, the systemmust be equipped with current injection means, and the system serverconfigured accordingly. The impedance calculations are performedperiodically, such as once every 24 hours, or can be calculated ondemand following a manual request. Following an impedance request,manual or automatic, the system stops monitoring each probe. The currentinjection means inject a current, preferably an AC current,simultaneously into each string. After approximately 20 seconds, threesubsequent samples of each of the AC components (voltage and current)are taken and the average value is calculated. The average componentsare then used to calculate the battery impedance following Ohm's law,i.e. Z_(b)=V_(bac)/I_(sac), where Z_(b) is the battery impedance,V_(bac) is the battery voltage AC component and I_(sac) is thecorresponding string current AC component. Since both AC components areaverage peak values, the impedance is calculated in Ohms. Each batteryimpedance can be displayed on a computer screen (in the case of a manualrequest for measurement) but only the values calculated automaticallyduring regular scanning are stored in the system server's database.

[0164] It is important to note that the impedance measurements of eachof the batteries is performed only in float conditions, so that thissection of the software is disabled when the lost current is outside thezone defined by the discharge level and the pre-set float current level.It should also be recognized that the impedance values can bemanipulated for graphical representation of the battery impedance trend.

[0165] The total energy discharged is calculated when the dischargecurrent exceeds a pre-set discharge level, as shown in FIG. 10.Following detection of a discharge, the energy is calculated using thefollowing formula:

P(kWh)=(V _(s) ×I _(s) ×T)/3600

[0166] where: P is the discharged energy in kWh with 0.1 kWh resolution;

[0167] V_(s) is the system voltage in Volts;

[0168] I_(s) is the system current in Amps; and

[0169] T is the time interval between subsequent samples, in seconds.

[0170] The discharge condition is detected by the polarity and level ofcurrent. Once a discharge condition is detected, the system serverperforms the following steps. A discharge condition is declaredfollowing the last probe reading. At this time, the system serverterminates all other routines expect those required to perform energycalculations. The serial port is cut off and therefore no communicationcan be established. The system server terminates the present cycle assoon as the data from the last probe is read. During the customerprogrammable Short Discharge Duration interval the system server willscan only the system voltage and current probes. Once the samples aretaken, the energy discharge is calculated with a sample rateapproximately equal to

1/(t×(1+string number))/per second

[0171] where t is approximately 0.2 s.

[0172] In each subsequent category, the sampling interval will equal thetime of a single scan of the entire system (which is approximately thetotal number of probes multiplied by 0.2 s).

[0173] Following the termination of discharge status, the calculateddischarge energy is added to the record of the corresponding dischargecategory (short or long) and the discharge count is increased by one.The number of discharges with a duration shorter than the pre-set timeinterval are kept in a separate log.

[0174] The discharge energy is calculated until the discharge currentcrosses the zero level and move into the charging zone. The energydischarged during each discharge event is added to the previous one tocreate a cumulative energy discharge value for the life of the systembeing monitored.

[0175] Once the measurements and calculations are performed, the systemserver manages the alarms associated therewith and manages the data soaccumulated.

[0176] The following alarms will be triggered when the appropriateconditions are met.

[0177] Cell overcharge alarm will be generated when the battery voltageexceeds a pre-set overcharge limit multiplied by the number of cells perbattery;

[0178] Cell undercharge alarm will be triggered when the battery voltagedrops below a pre-set cell undercharge limit multiplied by the number ofcells per battery;

[0179] Cell discharge alarm will be triggered when the battery voltagedrops below a pre-set cell discharge limit multiplied by the number ofcells per battery;

[0180] System overcharge alarm will be triggered when the system voltageexceeds a pre-set value of the system overcharge limit;

[0181] System undercharge alarm will be triggered when the systemvoltage exceeds a pre-set value of the system undercharge limit;

[0182] Ambient temperature alarm will be triggered when the measuredambient temperature exceeds a pre-set limit;

[0183] Thermal runaway alarm will be triggered when the differencebetween the internal temperature of the battery and the correspondingambient temperature exceeds a pre-determined limit;

[0184] Float current alarm will be triggered when a long term increasedfloat current exceeds a pre-set limit;

[0185] Impedance alarm will be triggered when the impedance of a batteryincreases above a pre-set threshold value;

[0186] Configurable customer alarms will be triggered when selectedvalues other than those previously mentioned exceed pre-determinedvalues;

[0187] Equipment failure alarm will be triggered when the systemserver's processor fails, or any of the probes fail.

[0188] These alarms are used to inform a user about the actual status ofthe battery system. In order to simplify the information provided to theuser, the preferred embodiment of the invention classifies alarms intotwo categories: major and minor. The alarms can be assigned a categoryby the user depending on the user's needs.

[0189] All alarms are logged into a history log in the system server.When the history log has been reviewed or downloaded to a remotelocation, the log can be cleared.

[0190] Major and Minor alarms activate respective LEDs, or other visualor audible signals, on the face of the system server. Alternatively,Major alarms only can activate a visual and an audible indicator. It isalso preferable if the system server is equipped with a modem that aMajor alarm initiates the auto-call function to report the alarm.

[0191] It should be noted that the thermal runaway alarm can beclassified as a major or a minor alarm. However, in any event, thethermal runaway will activate a LED on the system server.

[0192] The equipment alarm is preferably assigned a major alarmpriority, since equipment failure practically eliminates any monitoringby the system server. Again, if the system is provided with a modem, theequipment alarm will initiate the auto-call function.

[0193] Preferably, all the events which are defined as system alarms arerecorded in the history log using the following format: alarm name,status (ON/OFF), location (i.e. probe number), time of alarm and date.Preferably, the history log is organized in a first-in first-outconfiguration, so that-if the history log overflows, the first alarm isremoved once the new message causing the overflow is recorded.

[0194] Thus, it can be seen that the invention lies in an interfacedevice for interfacing at least one battery with a battery systemmonitor and to a battery system monitor incorporating the same. One ofthe aspects of the invention lies in the fact that the probes are“self-addressable”, so that each time a reset of the system occurs, theprobes can be automatically re-addressed. Furthermore, another aspect ofthe invention lies in the possibility to calculate the impedance of eachbattery by injecting an AC current into a whole string, and measuringthe corresponding AC voltage and current components at each batteryterminals. Furthermore, the invention also provides for methods forinitializing a plurality of probes, and for monitoring a plurality ofprobes in a battery monitoring system.

[0195] It should be equally clear from the above description that notall of the above-mentioned parameters, calculations and various otherfeatures need to be present in each battery monitoring system, or ineach interface device. Furthermore, persons skilled in this field willreadily recognize that a number of peripherals may be connected to thebattery monitoring system, such as a portable access/display unit, alocal LED display, a personal computer, a laptop computer or any kind ofmodem, or other communications, means.

[0196] Although the present invention has been explained hereinabove byway of a preferred embodiment thereof, it should be pointed out that anymodifications to this preferred embodiment within the scope of theappended claims is not deemed to alter or change the nature and scope ofthe present invention.

What is claimed is:
 1. An interface device for interfacing at least aportion of at least one string of batteries with a battery monitoringsystem, comprising: a) at least one probe means for respectively probingsaid portion of said at least one string, each of said at least oneprobe means including: i) a controllable sensing means for sensing aplurality of parameters of the corresponding portion; ii) acommunication means for communicating data to and from the controllablesensing means, the data including control signals sent from the batterymonitoring system to the controllable sensing means, and informationsignals relating to the parameters of the corresponding portion that areselected by the control signals; and iii) a memory for memorizing anaddress assigned to the corresponding probe means upon reception of aninitialization signal sent by the battery monitoring system via thecommunication means; and b) a bus for serially interconnecting thecommunication means of each of said at least one probe means to thebattery monitoring system in a daisy chain manner.
 2. An interfacedevice according to claim 1, wherein: a) said communication meansincludes a multiplexer, an analog to digital converter, controller meansfor controlling the operation of said probe means and optical insulationmeans for insulating said communication means from said bus means; andb) said bus is a five wire bus, where a first wire is used exclusivelyfor addressing purposes, a second wire is used as a broadcast inchannel, a third wire is used as a broadcast out channel, and a fourthand fifth wires are used for supplying voltage.
 3. An interface deviceaccording to claim 2, wherein: a) said sensing means of said probeincludes an AC conditioning section and an analog front end, said analogfront end being connected to said battery terminals and to saidmultiplexer of said communication means.
 4. An interface deviceaccording to claim 1, wherein said probe means are a battery performanceprobe, and said portion of said string include a positive and negativeterminal of a battery, and said probe means are connected to saidpositive and negative terminals of said battery.
 5. An interface deviceaccording to claim 1, wherein said probe means are a current probe, andsaid portion of said string include a shunt resistor, and said probemeans are connected to said shunt resistor.
 6. An interface deviceaccording to claim 1, wherein said probe means are a rectifier voltageprobe, and said portion of said string is said string as a whole havinga positive and negative terminal, and said probe means are connected tosaid positive and negative terminals of said string.
 7. A batterymonitoring system comprising; a) a plurality of batteries connected inseries to form at least one string of batteries; b) a plurality of probemeans for respectively probing a portion of said at least one string,each of said probe means including: i) a controllable sensing means forsensing a plurality of parameters of the corresponding portion of saidat least one string; ii) a communication means for communicating data toand from the controllable sensing means, the data including controlsignals and information signals relating to the parameters of thecorresponding portion of said at least one string that are selected bythe control signal; iii) a memory for memorizing an address assigned tothe corresponding probe means upon reception of an initializationsignal; iv) a bus for serially interconnecting the communication meansof each of said at least one probe means in a daisy chain manner; and c)a system server connected to said bus and configured to transmit aninitialization signal, to receive respective addresses from each of saidat least one probe means, to select one of said at least one probe, totransmit control signals to a selected one of said at least one probeand to receive information signals relating to the characteristics ofthe corresponding portion of said at least one string, memory means forstoring said information signals, calculating means for calculating aplurality of values relating to said characteristics and alarm means forraising an alarm when one or more of said values is outside apredetermined range.
 8. A battery monitoring system according to claim7, wherein: a) said communication means includes a multiplexer, ananalog to digital converter, microprocessor means for controlling theoperation of said probe means and optical insulation means forinsulating said communication means from said bus means; and b) said busis a five wire bus, where a first wire is used exclusively foraddressing purposes, a second wire is used as a broadcast in channel, athird wire is used as a broadcast out channel, and a fourth and fifthwires are used for supplying voltage.
 9. A battery monitoring systemaccording to claim 8, wherein: a) said sensing means of said probeincludes an AC conditioning section and an analog front end, said analogfront end being connected to said portion of said string and to saidmultiplexer of said communication means.
 10. A battery monitoring systemaccording to claim 7, wherein said probe means includes at least onebattery performance probe.
 11. A battery monitoring system according toclaim 10, wherein said probe means further includes at least one currentprobe.
 12. A battery monitoring system according to claim 10, whereinsaid probe means further includes at least one rectifier voltage probe.13. A battery monitoring system comprising: a) a plurality of batteriesconnected in series to form at least one string of batteries; b) aplurality of probe means for respectively probing one at least a portionof said at least one string, each of said probe means including: i) acontrollable sensing means for sensing a plurality of parameters of thecorresponding portion; ii) a communication means for communicating datato and from the controllable sensing means, the data including controlsignals and information signals relating to the parameters of thecorresponding portion that are selected by the control signal; iii) abus for serially interconnecting the communication means of each of saidat least one probe means in a daisy chain manner; c) at least onecurrent injection means connected to said at least one string forinjecting a current in said at least one string upon receipt of acontrol signal; and d) a system server connected to said bus andconfigured to select one of said at least one probe means, to transmitcontrol signals to a selected one of said at least one probe means andto receive information signals relating to the characteristics of thecorresponding portion, memory means for storing said informationsignals, calculating means for calculating a plurality of valuesrelating to said characteristics and alarm means for raising an alarmwhen one or more of said values is outside a predetermined range, saidsystem server being operatively connected to said at least one currentinjection means for sending a control signal to said current injectionmeans to inject a current in said at least one string.
 14. A batterymonitoring system according to claim 13, wherein said current that isinjected by said current injection means is an AC current.
 15. A batterymonitoring system according to claim 13, wherein said at least one probemeans includes at least one battery performance probe.
 16. A batterymonitoring system according to claim 15, wherein said at least one probemeans further includes a current probe for each of said at least onestring.
 17. A battery monitoring system according to claim 16, whereinsaid at least one probe means further includes a rectifier voltage probefor each of said at least one string.
 18. A method of initializing aplurality of probes in a battery monitoring system, the batterymonitoring system including: a) a plurality of batteries connected inseries to form at least one string of batteries; b) a plurality of probemeans for respectively probing one of said plurality of batteries, eachof said probe means including: i) a controllable sensing means forsensing a plurality of parameters of the corresponding battery; ii) acommunication means for communicating data to and from the controllablesensing means, the data including control signals and informationsignals relating to the parameters of the corresponding battery that areselected by the control signal; iii) a memory for memorizing an addressassigned to the corresponding battery upon reception of aninitialization signal; iv) a bus for serially interconnecting thecommunication means of each of said at least one probe means in a daisychain manner; and c) a system server connected to said bus andconfigured to transmit an initialization signal, to receive respectiveaddresses from each of said at least one probe means, to select one ofsaid at least one probe, to transmit control signals to a selected oneof said at least one probe and to receive information signals relatingto the characteristics of the corresponding battery, memory means forstoring said information signals, calculating means for calculating aplurality of values relating to said characteristics and alarm means forraising an alarm when one or more of said values is outside apredetermined range; the method comprising the steps of: a) sending aninitialize request on the bus means to all probes so that all probeserases their present address and set themselves in listen mode; b) foreach probe in each string: i) selecting a probe by setting a low voltageon a probe select line; ii) sending from said probe to the server anactive state confirmation; iii) sending an address to the said probe;iv) registering said address in said probe and acknowledging saidregistration; v) upon receipt of said acknowledgement, sending a signalto said probe to deselect itself and select the next probe in the chain;and c) performing each of said steps i) to v) for each of said probes ineach of said strings.
 19. A method for measuring the impedance of aplurality of batteries connected in series to form at least one stringof batteries, each of said batteries being provided with probe means formeasuring the voltage across each of said batteries respectively, themethod comprising the steps of: a) providing a current injection meansfor each of said at least one string of batteries; b) injecting acurrent in each of said strings; c) measuring the voltage across each ofsaid batteries; d) calculating the impedance of each of said batteriesby dividing said voltage by said current for each of said batteries. 20.A method according to claim 19 wherein said step of injecting a currentin each of said strings includes the step of injecting an AC current.